Patent GB-592030-A (GB)
Title: System for locating a radiated-signal reflector
IPC: G01S7/10
Filed: 1943-02-03
Abstract: 592,030. Radiolocation. HAZELTINE CORPORATION. Feb. 3, 1943, No. 1837. Convention date, March 3, 1942. [Class 40 (v)] [Also in Group XXXVIII] A radiolocation or supersonic sound system for indicating the bearing, and preferably the distance, of a reflecting object comprises means for tracing on an in. dicator, e.g. a cathode-ray tube, a series of radial lines each corresponding to a certain scanning angle, and means for producing an indication on one of the lines indicative of the angular direction of the object and, preferably of its distance. The scanning beam may be rotated by the bodily movement of a renector or, preferably, by feeding a fixed aerial array 15 ... 18 through delay circuits 19, 20, 21 with a frequency-modulated carrier, the directivity of the beam varying with the instantaneous frequency as in Specification 577,674. The directivity of the receiving aerial 39-42 is similarly controlled. The system is controlled by a pulse-generator, each, pulse of a series corresponding to a particular angle of transmission and to a particular radial line on the cathode-ray screen. In the system shown in Fig. 1, the scanning beam oscillates about a vertical axis through an angle of 90 degrees and the effective radial lines shown in full on the cathode-ray screen occupy a similar angle. In a modified system, Fig. 5 (not shown), scanning is effected over a complete circle by using four separate aerial systems, each covering 90 degrees. Transmitting, arrangements, Fig. 1. The carrier wave generator 14 is modulated in frequency by unit 13 under control of a sawtooth waveform from unit 12, the repetition frequency of which corresponds to the frequency of scanning, say 10 per second. The frequency of the carrier wave, and consequently the' directivity of the radiated wave, thus tends to vary linearly, but the generator 12 is inoperative except for short periods determined by the pulse generators 11, 25 and blocking and amplitude modulators 23, 26. Successive pulses of radiated energy thus vary in frequency and in direction, each pulse corresponding to a certain scanning angle. Receiving arrangements, Fig. 1. The directivity of the receiving aerial 39 ... 42 is varied, in synchronism with that of the transmitting aerial, by the frequency modulator 38, controlled (like 13) by the saw-tooth generator 12. The output of the receiver 37 is applied to the control electrode 35 of the cathode-ray tube ; the control electrode is also connected to the output of a square-wave generator 34 which extinguishes the part, shown in dotted lines, of all the radial lines traced on the screen. In order to trace the radial lines, the deflecting electrodes 28, 29 are connected* respectively to balanced modulators 32, 30. Modulator 30 is controlled by the saw-tooth generators 24, 12 of line frequency and scanning frequency respectively, and modulator 32 by the sawtooth generator 12 of line frequency and a parabolic-waveform generator 31 of scanning frequency. The outputs of generators 12 and 31 may be regarded as parts of two sine-wave voltages displaced by 90 degrees, which tend to rotate the cathode-ray beam in a circle at the slow scanning speed, but the beam is returned intermittently to the origin at a higher speed by the voltage from the generator 24; thus the beam traces a succession of radial lines under control of successive pulses from' generator 24, which synchronize with the' radiation of pulses of energy in different angular directions. Thus, energy reflected from a distant object increases the illumination at one point on the radial line corresponding to the direction of the object; the distance of the object is indicated by the distance of this point from the point at which the radial lines intersect. The cathode-ray screen may be associated, for viewing, with a map by a semitransparent mirror, Fig. 4 (not shown), or in other ways. The modified system. Figs: 5 and 6 (not shown), in which scanning is effected over a complete circle by using four separate aerials, each covering 90 degree's, operates on the same principle as Fig. 1, the circuits being modified to use four separate carrier-wave generators and associated frequency-modulators. These generators are energized in succession cyclically by a series of phase-displaced pulses derived from two sine-wave generators producing alternating currents displaced by 90 degrees. These currents are passed through shaping-units which produce square waves and the output of these units are applied to four "amplitude modulators" or combining circuits in such a way as to produce positive and negative phase displaced pulses in four circuits controlling the four carrier-wave generators, respectively. The four generators are frequency modulated through a predetermined frequency range individual to each unit. The invention may also be used with a radiated supersonic sound scanning beam, e.g. in detecting undersea craft.